Tip-derived artifacts remain one of the chief limitations of atomic force microscopy (AFM) when attempting to measure sub-nanometer structures. Carbon nanotubes represent ideal structures for use as AFM tips because of their small diameter, high aspect ratio and high strength.
Atomic force microscopes (AFM) are widely used to image and characterize various surfaces and also by the integrated circuit industry as a metrology tool. A typical AFM probe consists of a silicon or silicon nitride cantilever with a pyramidal-shaped tip. This tip now can be made as small as 10–20 nm, offering reasonable resolution. However, the large cone angle of the tip (30–35 deg.) makes it difficult for probing narrow and deep features such as trenches in integrated circuit manufacturing. Another inherent negative feature of AFM probes known in the art is that the tip is brittle thus its use in applications is limited. The tips are subject to breakage or may become blunt after only a limited use.
Carbon nanotube (CNT) probes have become an attractive alternative to AFM cantilevers. The CNT probe not only offers extraordinary nanometer scale resolution but is also robust, due to its high strength and the ability to retain structural integrity even after deformation within elastic limit. Carbon nanotube probes known in the art are provided either by manual attachment of a carbon nanotube to the tip of the AFM cantilever or by growing a carbon nanotube through a lithography and chemical vapor deposition process from the ends of the silicon tip of the AFM probe. The process of manually attaching carbon nanotubes to the tip of an AFM is time consuming and selects against the smallest nanotubes, limiting the quality of tips. The processes known in the art for growing carbon nanotubes from the ends of the silicon tip of the AFM probe are inherently complex, requiring multiple processing steps, which are not easily reproducible.
Accordingly, what is needed in the art is a simple, reliable and inexpensive technique for the high yield assembly of carbon nanotubes onto atomic force microscopy probes.